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<a name="1" href="#1">1</a>   <em class="jxr_comment">/*</em>
<a name="2" href="#2">2</a>   <em class="jxr_comment"> * To change this template, choose Tools | Templates</em>
<a name="3" href="#3">3</a>   <em class="jxr_comment"> * and open the template in the editor.</em>
<a name="4" href="#4">4</a>   <em class="jxr_comment"> */</em>
<a name="5" href="#5">5</a>   <strong class="jxr_keyword">package</strong> com.totsp.gwittir.client.util.compress;
<a name="6" href="#6">6</a>   
<a name="7" href="#7">7</a>   <strong class="jxr_keyword">import</strong> java.util.ArrayList;
<a name="8" href="#8">8</a>   <strong class="jxr_keyword">import</strong> java.util.HashMap;
<a name="9" href="#9">9</a>   <strong class="jxr_keyword">import</strong> java.util.Iterator;
<a name="10" href="#10">10</a>  
<a name="11" href="#11">11</a>  
<a name="12" href="#12">12</a>  <em class="jxr_javadoccomment">/**</em>
<a name="13" href="#13">13</a>  <em class="jxr_javadoccomment"> *</em>
<a name="14" href="#14">14</a>  <em class="jxr_javadoccomment"> * @author kebernet</em>
<a name="15" href="#15">15</a>  <em class="jxr_javadoccomment"> */</em>
<a name="16" href="#16">16</a>  <strong class="jxr_keyword">public</strong> <strong class="jxr_keyword">class</strong> <a href="../../../../../../com/totsp/gwittir/client/util/compress/HuffmanDecoder.html">HuffmanDecoder</a> {
<a name="17" href="#17">17</a>      ArrayList&lt;Byte&gt; binaryEncodedData;
<a name="18" href="#18">18</a>      HashMap&lt;Byte, String&gt; decodingBitMap = <strong class="jxr_keyword">new</strong> HashMap&lt;Byte, String&gt;();
<a name="19" href="#19">19</a>      HashMap&lt;String, Character&gt; huffDecodeTable = <strong class="jxr_keyword">new</strong> HashMap&lt;String, Character&gt;();
<a name="20" href="#20">20</a>      <em class="jxr_comment">//The following structure contains particulars as to how</em>
<a name="21" href="#21">21</a>      <em class="jxr_comment">// the original message was encoded, and must be received</em>
<a name="22" href="#22">22</a>      <em class="jxr_comment">// as an incoming parameter to the decode method along</em>
<a name="23" href="#23">23</a>      <em class="jxr_comment">// with the encoded message and the length of the</em>
<a name="24" href="#24">24</a>      <em class="jxr_comment">// original message.</em>
<a name="25" href="#25">25</a>      HashMap&lt;Character, String&gt; huffEncodeTable;
<a name="26" href="#26">26</a>      String decodedData = <span class="jxr_string">""</span>;
<a name="27" href="#27">27</a>      String stringDecodedData;
<a name="28" href="#28">28</a>  
<a name="29" href="#29">29</a>      <em class="jxr_comment">//Used to eliminate the extraneous characters on the end.</em>
<a name="30" href="#30">30</a>      <strong class="jxr_keyword">int</strong> rawDataLen;
<a name="31" href="#31">31</a>  
<a name="32" href="#32">32</a>      <em class="jxr_comment">//This method populates a lookup table that relates eight</em>
<a name="33" href="#33">33</a>      <em class="jxr_comment">// bits represented as a String to eight actual bits for</em>
<a name="34" href="#34">34</a>      <em class="jxr_comment">// all possible combinations of eight bits.  This is</em>
<a name="35" href="#35">35</a>      <em class="jxr_comment">// essentially a reverse lookup table relative to the</em>
<a name="36" href="#36">36</a>      <em class="jxr_comment">// encodingBitMap table that is used to encode the</em>
<a name="37" href="#37">37</a>      <em class="jxr_comment">// message.  The only difference between the two is a</em>
<a name="38" href="#38">38</a>      <em class="jxr_comment">// reversal of the key and the value in the HashMap</em>
<a name="39" href="#39">39</a>      <em class="jxr_comment">// that contains the table.</em>
<a name="40" href="#40">40</a>      <strong class="jxr_keyword">void</strong> buildDecodingBitMap() {
<a name="41" href="#41">41</a>          <strong class="jxr_keyword">for</strong> (<strong class="jxr_keyword">int</strong> cnt = 0; cnt &lt;= 255; cnt++) {
<a name="42" href="#42">42</a>              StringBuffer workingBuf = <strong class="jxr_keyword">new</strong> StringBuffer();
<a name="43" href="#43">43</a>  
<a name="44" href="#44">44</a>              <strong class="jxr_keyword">if</strong> ((cnt &amp; 128) &gt; 0) {
<a name="45" href="#45">45</a>                  workingBuf.append(<span class="jxr_string">"1"</span>);
<a name="46" href="#46">46</a>              } <strong class="jxr_keyword">else</strong> {
<a name="47" href="#47">47</a>                  workingBuf.append(<span class="jxr_string">"0"</span>);
<a name="48" href="#48">48</a>              }
<a name="49" href="#49">49</a>  
<a name="50" href="#50">50</a>              <strong class="jxr_keyword">if</strong> ((cnt &amp; 64) &gt; 0) {
<a name="51" href="#51">51</a>                  workingBuf.append(<span class="jxr_string">"1"</span>);
<a name="52" href="#52">52</a>              } <strong class="jxr_keyword">else</strong> {
<a name="53" href="#53">53</a>                  workingBuf.append(<span class="jxr_string">"0"</span>);
<a name="54" href="#54">54</a>              }
<a name="55" href="#55">55</a>  
<a name="56" href="#56">56</a>              <strong class="jxr_keyword">if</strong> ((cnt &amp; 32) &gt; 0) {
<a name="57" href="#57">57</a>                  workingBuf.append(<span class="jxr_string">"1"</span>);
<a name="58" href="#58">58</a>              } <strong class="jxr_keyword">else</strong> {
<a name="59" href="#59">59</a>                  workingBuf.append(<span class="jxr_string">"0"</span>);
<a name="60" href="#60">60</a>              }
<a name="61" href="#61">61</a>  
<a name="62" href="#62">62</a>              <strong class="jxr_keyword">if</strong> ((cnt &amp; 16) &gt; 0) {
<a name="63" href="#63">63</a>                  workingBuf.append(<span class="jxr_string">"1"</span>);
<a name="64" href="#64">64</a>              } <strong class="jxr_keyword">else</strong> {
<a name="65" href="#65">65</a>                  workingBuf.append(<span class="jxr_string">"0"</span>);
<a name="66" href="#66">66</a>              }
<a name="67" href="#67">67</a>  
<a name="68" href="#68">68</a>              <strong class="jxr_keyword">if</strong> ((cnt &amp; 8) &gt; 0) {
<a name="69" href="#69">69</a>                  workingBuf.append(<span class="jxr_string">"1"</span>);
<a name="70" href="#70">70</a>              } <strong class="jxr_keyword">else</strong> {
<a name="71" href="#71">71</a>                  workingBuf.append(<span class="jxr_string">"0"</span>);
<a name="72" href="#72">72</a>              }
<a name="73" href="#73">73</a>  
<a name="74" href="#74">74</a>              <strong class="jxr_keyword">if</strong> ((cnt &amp; 4) &gt; 0) {
<a name="75" href="#75">75</a>                  workingBuf.append(<span class="jxr_string">"1"</span>);
<a name="76" href="#76">76</a>              } <strong class="jxr_keyword">else</strong> {
<a name="77" href="#77">77</a>                  workingBuf.append(<span class="jxr_string">"0"</span>);
<a name="78" href="#78">78</a>              }
<a name="79" href="#79">79</a>  
<a name="80" href="#80">80</a>              <strong class="jxr_keyword">if</strong> ((cnt &amp; 2) &gt; 0) {
<a name="81" href="#81">81</a>                  workingBuf.append(<span class="jxr_string">"1"</span>);
<a name="82" href="#82">82</a>              } <strong class="jxr_keyword">else</strong> {
<a name="83" href="#83">83</a>                  workingBuf.append(<span class="jxr_string">"0"</span>);
<a name="84" href="#84">84</a>              }
<a name="85" href="#85">85</a>  
<a name="86" href="#86">86</a>              <strong class="jxr_keyword">if</strong> ((cnt &amp; 1) &gt; 0) {
<a name="87" href="#87">87</a>                  workingBuf.append(<span class="jxr_string">"1"</span>);
<a name="88" href="#88">88</a>              } <strong class="jxr_keyword">else</strong> {
<a name="89" href="#89">89</a>                  workingBuf.append(<span class="jxr_string">"0"</span>);
<a name="90" href="#90">90</a>              }
<a name="91" href="#91">91</a>  
<a name="92" href="#92">92</a>              decodingBitMap.put((byte) (cnt), workingBuf.toString());
<a name="93" href="#93">93</a>          } <em class="jxr_comment">//end for loop</em>
<a name="94" href="#94">94</a>      } <em class="jxr_comment">//end buildDecodingBitMap()</em>
<a name="95" href="#95">95</a>        <em class="jxr_comment">//-----------------------------------------------------//</em>
<a name="96" href="#96">96</a>  
<a name="97" href="#97">97</a>      <em class="jxr_comment">//This method creates a Huffman decoding table by</em>
<a name="98" href="#98">98</a>      <em class="jxr_comment">// swapping the keys and the values from the Huffman</em>
<a name="99" href="#99">99</a>      <em class="jxr_comment">// encoding table received as an incoming parameter by</em>
<a name="100" href="#100">100</a>     <em class="jxr_comment">// the decode method.</em>
<a name="101" href="#101">101</a>     <strong class="jxr_keyword">void</strong> buildHuffDecodingTable() {
<a name="102" href="#102">102</a>         Iterator&lt;Character&gt; enumerator = huffEncodeTable.keySet().iterator();
<a name="103" href="#103">103</a> 
<a name="104" href="#104">104</a>         <strong class="jxr_keyword">while</strong> (enumerator.hasNext()) {
<a name="105" href="#105">105</a>             Character nextKey = enumerator.next();
<a name="106" href="#106">106</a>             String nextString = huffEncodeTable.get(nextKey);
<a name="107" href="#107">107</a>             huffDecodeTable.put(nextString, nextKey);
<a name="108" href="#108">108</a>         } <em class="jxr_comment">//end while</em>
<a name="109" href="#109">109</a>     } <em class="jxr_comment">//end buildHuffDecodingTable()</em>
<a name="110" href="#110">110</a>       <em class="jxr_comment">//-----------------------------------------------------//</em>
<a name="111" href="#111">111</a> 
<a name="112" href="#112">112</a>     <em class="jxr_comment">//-----------------------------------------------------//</em>
<a name="113" href="#113">113</a> 
<a name="114" href="#114">114</a>     <em class="jxr_comment">//This method receives a Huffman-encoded message along</em>
<a name="115" href="#115">115</a>     <em class="jxr_comment">// with a data structure containing particulars as to how</em>
<a name="116" href="#116">116</a>     <em class="jxr_comment">// the original message was encoded and the length of the</em>
<a name="117" href="#117">117</a>     <em class="jxr_comment">// original message.  It decodes the original message and</em>
<a name="118" href="#118">118</a>     <em class="jxr_comment">// returns the decoded version as a String object.</em>
<a name="119" href="#119">119</a>     <strong class="jxr_keyword">public</strong> String decode(byte[] encodedData,
<a name="120" href="#120">120</a>         HashMap&lt;Character, String&gt; huffEncodeTable, <strong class="jxr_keyword">int</strong> rawDataLen) {
<a name="121" href="#121">121</a>         <em class="jxr_comment">//Save the incoming parameters.</em>
<a name="122" href="#122">122</a>         ArrayList&lt;Byte&gt; encodedDataList = <strong class="jxr_keyword">new</strong> ArrayList&lt;Byte&gt;(encodedData.length);
<a name="123" href="#123">123</a>         <strong class="jxr_keyword">for</strong>(byte b: encodedData){
<a name="124" href="#124">124</a>             encodedDataList.add(b);
<a name="125" href="#125">125</a>         }
<a name="126" href="#126">126</a>         <strong class="jxr_keyword">this</strong>.binaryEncodedData = encodedDataList;
<a name="127" href="#127">127</a>         <strong class="jxr_keyword">this</strong>.huffEncodeTable = huffEncodeTable;
<a name="128" href="#128">128</a>         <strong class="jxr_keyword">this</strong>.rawDataLen = rawDataLen;
<a name="129" href="#129">129</a> 
<a name="130" href="#130">130</a>         <em class="jxr_comment">//Create a decoding bit map, which is essentially the</em>
<a name="131" href="#131">131</a>         <em class="jxr_comment">// reverse of the encoding bit map that was used to</em>
<a name="132" href="#132">132</a>         <em class="jxr_comment">// encode the original message.</em>
<a name="133" href="#133">133</a>         buildDecodingBitMap();
<a name="134" href="#134">134</a> 
<a name="135" href="#135">135</a>         <em class="jxr_comment">//Decode the encoded message from a binary</em>
<a name="136" href="#136">136</a>         <em class="jxr_comment">// representation to a String of 1 and 0 characters</em>
<a name="137" href="#137">137</a>         <em class="jxr_comment">// that represent the actual bits in the encoded</em>
<a name="138" href="#138">138</a>         <em class="jxr_comment">// message.  Also, for illustration purposes only,</em>
<a name="139" href="#139">139</a>         <em class="jxr_comment">// this method may optionally display the String.</em>
<a name="140" href="#140">140</a>         decodeToBitsAsString();
<a name="141" href="#141">141</a> 
<a name="142" href="#142">142</a>         <em class="jxr_comment">//Create a Huffman decoding table by swapping the keys</em>
<a name="143" href="#143">143</a>         <em class="jxr_comment">// and values from the Huffman encoding table received</em>
<a name="144" href="#144">144</a>         <em class="jxr_comment">// as an incoming parameter by the decode method.</em>
<a name="145" href="#145">145</a>         buildHuffDecodingTable();
<a name="146" href="#146">146</a> 
<a name="147" href="#147">147</a>         <em class="jxr_comment">//Decode the String containing only 1 and 0 characters</em>
<a name="148" href="#148">148</a>         <em class="jxr_comment">// that represent the bits in the encoded message. This</em>
<a name="149" href="#149">149</a>         <em class="jxr_comment">// produces a replica of the original message that was</em>
<a name="150" href="#150">150</a>         <em class="jxr_comment">// subjected to Huffman encoding.  Write the resulting</em>
<a name="151" href="#151">151</a>         <em class="jxr_comment">// decoded message into a String object referred to by</em>
<a name="152" href="#152">152</a>         <em class="jxr_comment">// decoded data.</em>
<a name="153" href="#153">153</a>         decodeStringBitsToCharacters();
<a name="154" href="#154">154</a> 
<a name="155" href="#155">155</a>         <em class="jxr_comment">//Return the decoded message.  Eliminate the extraneous</em>
<a name="156" href="#156">156</a>         <em class="jxr_comment">// characters from the end of the message on the basis</em>
<a name="157" href="#157">157</a>         <em class="jxr_comment">// of the known length of the original message.</em>
<a name="158" href="#158">158</a>         <strong class="jxr_keyword">return</strong> decodedData.substring(0, rawDataLen);
<a name="159" href="#159">159</a>     } <em class="jxr_comment">//end decode method</em>
<a name="160" href="#160">160</a>       <em class="jxr_comment">//-----------------------------------------------------//</em>
<a name="161" href="#161">161</a> 
<a name="162" href="#162">162</a>     <em class="jxr_comment">//The method begins with an empty StringBuffer object</em>
<a name="163" href="#163">163</a>     <em class="jxr_comment">// referred to by the variable named workBuf and another</em>
<a name="164" href="#164">164</a>     <em class="jxr_comment">// empty StringBuffer object referred to by the variable</em>
<a name="165" href="#165">165</a>     <em class="jxr_comment">// named output.  The StringBuffer object referred to by</em>
<a name="166" href="#166">166</a>     <em class="jxr_comment">// output is used to construct the decoded message.  The</em>
<a name="167" href="#167">167</a>     <em class="jxr_comment">// StringBuffer object referred to by workBuf is used as</em>
<a name="168" href="#168">168</a>     <em class="jxr_comment">// a temporary holding area for substring data.</em>
<a name="169" href="#169">169</a>     <em class="jxr_comment">//The method reads the String containing only 1 and 0</em>
<a name="170" href="#170">170</a>     <em class="jxr_comment">// characters that represent the bits in the encoded</em>
<a name="171" href="#171">171</a>     <em class="jxr_comment">// message (stringDecodedData).  The characters are read</em>
<a name="172" href="#172">172</a>     <em class="jxr_comment">// from this string one character at a time.  As each new</em>
<a name="173" href="#173">173</a>     <em class="jxr_comment">// character is read, it is appended to the StringBuffer</em>
<a name="174" href="#174">174</a>     <em class="jxr_comment">// object referred to by workBuf.</em>
<a name="175" href="#175">175</a>     <em class="jxr_comment">//As each new character is appended to the StringBuffer</em>
<a name="176" href="#176">176</a>     <em class="jxr_comment">// object, a test is performed to determine if the</em>
<a name="177" href="#177">177</a>     <em class="jxr_comment">// current contents of the StringBuffer object match one</em>
<a name="178" href="#178">178</a>     <em class="jxr_comment">// of the keys in a lookup table that relates strings</em>
<a name="179" href="#179">179</a>     <em class="jxr_comment">// representing Huffman bitcodes to characters in the</em>
<a name="180" href="#180">180</a>     <em class="jxr_comment">// original message.</em>
<a name="181" href="#181">181</a>     <em class="jxr_comment">//When a match is found, the value  associated with that</em>
<a name="182" href="#182">182</a>     <em class="jxr_comment">// key is extracted and appended to the StringBuffer</em>
<a name="183" href="#183">183</a>     <em class="jxr_comment">// object referred to by output.  Thus, the output text</em>
<a name="184" href="#184">184</a>     <em class="jxr_comment">// is built up one character at a time.</em>
<a name="185" href="#185">185</a>     <em class="jxr_comment">//Having processed the matching key, A new empty</em>
<a name="186" href="#186">186</a>     <em class="jxr_comment">// StringBuffer object is instantiated, referred to by</em>
<a name="187" href="#187">187</a>     <em class="jxr_comment">// workBuf, and the process of reading, appending, and</em>
<a name="188" href="#188">188</a>     <em class="jxr_comment">// testing for a match is repeated until all of the</em>
<a name="189" href="#189">189</a>     <em class="jxr_comment">// characters in the string that represents the bits in</em>
<a name="190" href="#190">190</a>     <em class="jxr_comment">// the encoded message have been processed.  At that</em>
<a name="191" href="#191">191</a>     <em class="jxr_comment">// point, the StringBuffer object referred to by output</em>
<a name="192" href="#192">192</a>     <em class="jxr_comment">// contains the entire decoded message.  It is converted</em>
<a name="193" href="#193">193</a>     <em class="jxr_comment">// to type String and written into the object referred to</em>
<a name="194" href="#194">194</a>     <em class="jxr_comment">// by decodedData.  Then the method returns with the task</em>
<a name="195" href="#195">195</a>     <em class="jxr_comment">// of decoding the encoded message having been completed.</em>
<a name="196" href="#196">196</a>     <strong class="jxr_keyword">void</strong> decodeStringBitsToCharacters() {
<a name="197" href="#197">197</a>         StringBuffer output = <strong class="jxr_keyword">new</strong> StringBuffer();
<a name="198" href="#198">198</a>         StringBuffer workBuf = <strong class="jxr_keyword">new</strong> StringBuffer();
<a name="199" href="#199">199</a> 
<a name="200" href="#200">200</a>         <strong class="jxr_keyword">for</strong> (<strong class="jxr_keyword">int</strong> cnt = 0; cnt &lt; stringDecodedData.length(); cnt++) {
<a name="201" href="#201">201</a>             workBuf.append(stringDecodedData.charAt(cnt));
<a name="202" href="#202">202</a> 
<a name="203" href="#203">203</a>             <strong class="jxr_keyword">if</strong> (huffDecodeTable.containsKey(workBuf.toString())) {
<a name="204" href="#204">204</a>                 output.append(huffDecodeTable.get(workBuf.toString()));
<a name="205" href="#205">205</a>                 workBuf = <strong class="jxr_keyword">new</strong> StringBuffer();
<a name="206" href="#206">206</a>             } <em class="jxr_comment">//end if</em>
<a name="207" href="#207">207</a>         } <em class="jxr_comment">//end for loop</em>
<a name="208" href="#208">208</a> 
<a name="209" href="#209">209</a>         decodedData = output.toString();
<a name="210" href="#210">210</a>     }
<a name="211" href="#211">211</a> 
<a name="212" href="#212">212</a>     <em class="jxr_comment">//This method decodes the encoded message from a binary</em>
<a name="213" href="#213">213</a>     <em class="jxr_comment">// representation to a String of 1 and 0 characters that</em>
<a name="214" href="#214">214</a>     <em class="jxr_comment">// represent the actual bits in the encoded message.</em>
<a name="215" href="#215">215</a>     <em class="jxr_comment">// Also, for illustration purposes only, this method</em>
<a name="216" href="#216">216</a>     <em class="jxr_comment">// may optionally display that String.</em>
<a name="217" href="#217">217</a>     <strong class="jxr_keyword">void</strong> decodeToBitsAsString() {
<a name="218" href="#218">218</a>         StringBuffer workingBuf = <strong class="jxr_keyword">new</strong> StringBuffer();
<a name="219" href="#219">219</a> 
<a name="220" href="#220">220</a>         <strong class="jxr_keyword">for</strong> (Byte element : binaryEncodedData) {
<a name="221" href="#221">221</a>             byte wholeByte = element;
<a name="222" href="#222">222</a>             workingBuf.append(decodingBitMap.get(wholeByte));
<a name="223" href="#223">223</a>         } <em class="jxr_comment">//end for-each</em>
<a name="224" href="#224">224</a> 
<a name="225" href="#225">225</a>         <em class="jxr_comment">//Convert from StringBuffer to String</em>
<a name="226" href="#226">226</a>         stringDecodedData = workingBuf.toString();
<a name="227" href="#227">227</a> 
<a name="228" href="#228">228</a>         <em class="jxr_comment">//For illustration purposes only, enable the following</em>
<a name="229" href="#229">229</a>         <em class="jxr_comment">// two statements to display the String containing 1</em>
<a name="230" href="#230">230</a>         <em class="jxr_comment">// and 0 characters that represent the bits in the</em>
<a name="231" href="#231">231</a>         <em class="jxr_comment">// encoded message.</em>
<a name="232" href="#232">232</a>     } <em class="jxr_comment">//end decodeToBitsAsString</em>
<a name="233" href="#233">233</a>       <em class="jxr_comment">//-----------------------------------------------------//</em>
<a name="234" href="#234">234</a> }
</pre>
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